The invention relates to a force measuring cell with a force sensor in the form of a bendable support, wherein one end of the support is in the form of a base piece which is rigid with respect to bending, and the other end of the support is in the form of a load-receiving element, also rigid with respect to bending, wherewith the load-receiving element is connected to the base piece by means of two elastically bendable link members with bendable segments, which segments are characterized by a weakening of the material, and the force measuring cell is provided with expansion-measuring strips, e.g. strain gauges, disposed on the bendable segments on at least one of the link members, for generating an electric signal in accordance with the force being measured.
Force measuring cells with force sensors of the bendable support type are known, for example in U.S. Pat. Nos. 4,107,985 and 4,143,727. In addition, force measuring cells are commercially available in which the strain gauge elements are disposed on the bendable segments of the elastically bendable link members.
In the known force sensors of this type, the mean material thickness of the two bendable segments of an elastically bendable link member is the same. The result of this is that when the force sensor is stressed, the stresses on the two bendable segments of a link member are unequal in magnitude. In the event of ideal parallel guiding of the load-receiving elelments with respect to the base part, it would be possible to achieve a condition in which equal bending moments would be developed on both bendable segments of each link member. However, in a practical embodiment of the bendable support, wherein the link members have a certain degree of stiffness, the bending moment of the entire bendable support is superimposed over these individual bending moments. The result is a higher bending moment on the bendable segments of the link member, which bendable segments are disposed near the base part--higher than on the bendable segments disposed near the load-receiving elements, and the influence of the superimposed bending moment increases as the stiffness of the link members increases.
The non-uniform loading of the bendable segments has the consequence that theload-bearing capability of the force sensor is limited by the tolerable stress on the more heavily loaded bendable segments, while the load range of the less heavily loaded bendable segments is not completely utilized. In addition, there is a hazard that the stress on the more heavily loaded bendable segments will exceed the tolerable level. There is no assurance that the desired proportionality between the force being measured and the electrical signal corresponding to said force will be maintained, or that the required protection against overloading will be provided, under these conditions.